Open AccessMethionine oxidation and its effect on the stability of a reconstituted subunit of the light‐harvesting complex from Rhodospirillum rubrum
Author(s) -
Wang ZhengYu,
Shimonaga Masahiro,
Muraoka Yoshiyuki,
Kobayashi Masayuki,
Nozawa Tsunenori
Publication year - 2001
Publication title -
european journal of biochemistry
Language(s) - English
Resource type - Journals
eISSN - 1432-1033
pISSN - 0014-2956
DOI - 10.1046/j.1432-1327.2001.02234.x
Subject(s) - rhodospirillum rubrum , chemistry , methionine , protein subunit , methionine sulfoxide , biochemistry , amino acid , enzyme , gene
An additional component in the purified core light‐harvesting complex (LH1) from wild‐type purple photosynthetic bacterium Rhodospirillum rubrum has been identified as an oxidized species of α‐polypeptide by MALDI‐TOF mass spectrometry. This component appears as a slightly earlier‐eluting peak in the RP‐HPLC chromatogram compared with the authentic α‐polypeptide. The oxidation site has been determined to be the N‐terminal methionine residue by high‐resolution NMR spectroscopy, where the methionine is oxidized to methionine sulfoxide in a diastereoisomeric form. Interconversion between the oxidized and authentic α‐polypeptides has been confirmed by selective oxidation and reduction. The oxidative modification of methionine is shown to have discernible effects on the ability to form B820 subunit with β‐polypeptide and bacteriochlorophyll a , and on the stability of the reconstituted B820 subunit. Both the ability and the stability for the samples using the oxidized α‐polypeptide are moderately reduced, indicating that the oxidation‐induced conformational change in the N‐terminal domain of α‐polypeptide may affect the pigment‐binding environment through a long‐range interaction. The MALDI‐TOF mass results also reveal that the N‐terminus of α‐polypeptide is formylated and no phosphorylation has occurred in this polypeptide.